In traditional circuit-switched voice networks, a test commonly referred to as a “Draw and Break Dialtone” (DBDT) test is provided to assist a craft person (e.g., network technician) operating the network in sectionalizing “no-dialtone” customer complaints. The test includes first causing a subscriber's line to go off-hook (a loop closure), and then listening and detecting voice-frequency information from the subscriber's line. The craft person qualifies the received voice-frequency information as dial-tone and only dial-tone. The craft person then causes a dial-pulse sequence or dual-tone multi-frequency (DTMF) digit sequence to be emitted from a subscriber's line toward the circuit switch. In a functioning network, the dial-pulse sequence is expected to cause the dial tone to cease. Thus, the craft person verifies that the dial-tone was removed in response to the detection of the dial-pulse or DTMF sequence activity. Upon completion of this test, the subscriber's line is restored to its normal idle state, and the craft person records the results of the test.
In typical circuit-switched networks, a voice-frequency (VF) bearer information channel carries a plurality of discrete digital samples representing an audio signal corresponding to a call, and a signaling channel carries administrative data regarding the call. Both the bearer channel and signaling channel travel over the same logical channel, which is caused to be automatically created by the circuit-switch in response to a subscriber loop-closure event. Thus, the DBDT test, when executed successfully, is a fair and reliable test of both the signaling and VF bearer channel of the subscriber's circuit. Failure of the circuit switch to emit a dial-tone toward a subscriber line in response to a loop-closure event within a prescribed amount of time is cause for a corrective action on the part of the network operator. Likewise, failure of the circuit-switch to remove the dial-tone within a prescribed amount of time after a dial sequence is also a cause for a corrective action on the part of the network operator.